Theft is frequently a problem in retail stores as well as in other environments. In some environments, it is desirable to track objects. To address these issues, electronic article surveillance (EAS) systems are installed. Generally, in EAS systems, electronic tags, labels, or similarly titled electronic devices are placed on objects to be protected, or monitored. These EAS tags, or devices, are capable of generating a signal to reply back to the broader EAS system. The broader EAS system creates interrogation fields which stimulate the EAS tags to produce reply signals in response to the interrogation fields. These responding signals from the EAS tags, indicate that an EAS tag, and the object to which it is attached, are in an interrogation field.
These interrogation fields are frequently set up at exits or entries to an area that is being monitored or protected. Frequently, the antennas that are used to generate the interrogation fields and to monitor for tag signals are housed within pedestals that are placed to each side of an exit. However, these antennas and their controlling electronics can be positioned overhead or within the floor in the area close to the exit.
The controlling electronics for these antennas generate a signal which is transmitted by the antennas and creates the interrogation field. This field energizes or stimulates tags that are passing through the interrogation field, or zone. The tags then produce a signal in response to the interrogation field. This signal from the tags may be created by the energy of the field itself, or the tags may have on board power supplies and electronics that reply to the interrogation field. The interrogation field is cycled for periods of transmission and monitoring. The interrogation field initially cycles and broadcast out into the zone being monitored and then the interrogation field is stopped. The antennas of the EAS system then monitor for a tag signal. If a tag signal is detected, it is assumed that the tag is improperly in the zone being monitored by the interrogation field, and the EAS system determines that an alarm condition is in effect. The EAS system can then generate an alarm, either an optical alarm such as flashing lights, an audible alarm such as bells, etc., or a system alarm that is broadcast to operator stations.
EAS tags, or devices, are attached to objects by various methods. The method used depends on the type of object being protected and determines the shape of the EAS device. As one example, EAS tags for clothing frequently employ a tack to maintain the EAS tag on the article of clothing. Other applications use different methods which leads to EAS tags having different physical characteristics. For goods contained in a box, the EAS tag is attached to the box. Some EAS tags employ an adhesive to maintain the tag on the box and these may also employ a switch to monitor the continued attachment of the EAS tag on the box. If the box is enclosed in plastic wrapping, thieves may remove the EAS device from the box and maintain the wrapping on the adhesive, and thus defeat the switch.